1. Field of the Invention
The present invention relates to an apparatus for etching the front surface of a wafer one by one by centrifugal force, where the wafer is rotated while an etching solution is supplied onto the front surface of the wafer; and to a method therefor.
2. Description of the Related Art
In general, the process for manufacturing a semiconductor wafer comprises the steps of obtaining wafers by cutting and slicing out of a single crystal ingot, and chamfering the respective wafers, mechanical grinding (lapping), etching, mirror-polishing, and cleaning, thereby producing a wafer with highly precise flatness. The wafer, which has been subjected to the steps for mechanical processing, such as block-cutting, rounding, slicing, and lapping, has a damaged layer (i.e., a work-degenerated layer) on the surface thereof. In the process for device production, such a work-degenerated layer causes crystal defects, such as slip dislocation, and the mechanical strength of the wafer is then decreased. In addition, it has adverse effects on electric characteristics. Therefore, the work-degenerated layer should be completely removed. For removing such a work-degenerated layer, an etching process is carried out. There are two types of etching: dip-etching and single wafer etching.
Among the etching processes, the single wafer etching has been regarded as the most suitable etching process, which enables the control of the texture-size and surface roughness of a large-sized wafer. The single wafer etching is a process comprising dropping an etching solution onto the front surface of a flattened single wafer and rotating (spinning) the wafer to spread out the dripped etching solution over the front surface of the wafer. The etching solution supplied on the wafer is spread out over the surface of the wafer from a supplied point by centrifugal force caused by spinning the wafer, and finally reaches the edge of the wafer, so that the edge thereof as well as the front surface of that can be also etched at the same time. Furthermore, most of the etching solution supplied is blown off from the edge thereof by centrifugal force and then collected into a cup or the like arranged on an etching device.
However, in the single wafer etching, the etching solution is quantitatively dripped through a single supply nozzle, so that etching amount may vary. As a result, the front and back surfaces of a silicon wafer, subjected to the etching process, have deficiencies that the flatness of the wafer cannot be maintained after the flattening process including lapping and grinding. In addition, the desired surface roughness of the wafer cannot be obtained. Therefore, for improving the flatness and surface roughness thereof, a large amount of grinding margin is required in the mirror polishing process, so that the subsequent steps in mirror polishing will bear a heavy burden.
Therefore, as a process for manufacturing a semiconductor wafer that can effectively remove a processing-strained layer caused by mechanical grinding and retain the flatness of the wafer, there is disclosed one including the following steps; slicing a silicon single crystal ingot; chamfering the end face of the sliced wafer; flattening at least the front surface thereof obtained by slicing the semiconductor ingot by means of surface grinding or lapping; spin-etching the flattened front surface thereof; and polishing the etched front surface of the wafer into a mirror surface (e.g., see Patent Document 1).
Patent Document 1
Japanese Unexamined Patent Application Publication No. 11-135464 (Claim 1, FIG. 1)
However, the process disclosed in Patent Document 1 causes grinding traces and undulations on the wafer surface by holding the wafer at the time of grinding by mechanical grinding or the like in the flattening process. Therefore, a large amount of grinding margin is required not only for removing the processing-strained layer but also removing the grinding traces and undulations in the steps subsequent to the flattening process. Thus, the grinding process bears a heavy burden.